<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<META content="MSHTML 6.00.2800.1106" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT face=Arial size=2><FONT size=4>
<P>Hi Guys</P>
<P>Seemed to have opened a can of worms here. My thanks to all those who have
contributed to the discussion. I’m not generally responding to individual inputs
because there are many common points.</P>
<P>It has been suggested that the 300bd APRS signals can be considered both as
FM or AM signals. Dealing with the FM approach first using Carson’s Rule we have
that 98% of the power will lie within the bandwidth:</P>
<P>Bt=2(pF+Fm)</P>
<P>Where Bt = bandwidth, pF = deviation & Fm = modulating frequency</P>
<P>pF = 100Hz (being half the tone spacing) & Fm = 150Hz (being half the
baud rate)</P>
<P>Bt = 2(100+150) = 500Hz</P>
<P>This would sit neatly in the requirement of the 500Hz bandwidth requirement
but FM signals have sidebands that go on ad infinitum, albeit declining rapidly.
While the first sideband at + & -150Hz would be within the 500Hz bandwidth
the second at + & - 300Hz would not and it would be only some 20% of the
carrier. This would not fit in with the UK license requirement ‘that not more
than 1% of the mean power of the transmission falls outside the nominal
modulated carrier bandwidth’. In any event the argument is flawed in that an FM
signal only has one carrier that moves between the deviation limits not two as
suggested.</P>
<P>Alternatively we have the logical approach suggested by Steve, K9DCI,
considering that the two tones are two separate carriers modulated by the 150Hz
signals. If the 150Hz signals were pure sine waves we would have side bands at
–250 & +50Hz for the lower tone and –50 & +250Hz for the higher tone.
Again this would fit neatly into the 500Hz bandwidth requirement but with the
150Hz modulation not being pure sinewave there will be sidebands generated by
the harmonics. Bearing in mind that the main sidebands will already be 25% down
on the carriers and any sidebands generated by harmonics, that with square waves
will be odd harmonics, will be further reduced.</P>
<P>If I’m talking crap no doubt someone will put me straight.</P>
<P>Those of you who sit States side of the pond should not try and relate to the
situation here in Europe. Mobile APRS operation and the tracking of in the UK
and the rest of Europe is not the predominant activity. At the time of writing I
have the following stations displayed:-</P>
<P>
Mobiles Others</P>
<P>2m
16
23</P>
<P>20m
0
4</P>
<P>30m
6
19</P>
<P>Many of us use APRS as a straight communications tool. Among the advantages
the ability to see who is QRV without the need to trawl the band and messages
can be left if the operator is not at the keyboard.</P>
<P>Prior to his premature silent key, a ham in Scotland and I, near London, used
to have a regular exchange of messages, usually via a digi in Switzerland.
I have recently had a email from a ham in Germany expressing his regret that I
no longer ran a digi on 30m because it provided him with links during his mobile
excursions through the length and breadth of Europe.</P>
<P>With regards to propagation on HF, yes if conditions are right of course
signals will be heard. Unless you sit in the skip distance that is. My friend
G0IQK and I are 13 miles apart. We cannot always communicate directly on 2m and
never on 30m. For that we have to rely on digies on mainland Europe. Also bear
in mind that we do not have a KW to play with. As a full license I am limited to
400W PEP, Intermediate licenses 50W PEP and Novice license 10W PEP. Not that I
could even run at the maximum I’m allowed because I am surrounded by domestic
TVs and radios of crap design the owners of which would have the Regulator
around my ears.</P>
<P>With regard to Igates, putting aside my own negative views for the moment,
internet is not available throughout Europe. Even in the UK there are countless
places where it is still not available or only as a slow dial up. Our government
is suggesting that they may levy about $10 on our TV license, yes we pay about
$200 a year for the privilege of owning a TV set even if it’s off air, to pay
for a broadband roll out. In the UK again we have to apply for a Notice of
Variation if we wish to run an Igate. And phone hook ups forget it, not allowed
at all. While I’m talking Igates, I dread the thought of two way Igates surely
worse than HF digies.</P>
<P>I was pleased to note Keith’s (VE7GDH) comments about my article on </FONT><A
href="http://www.apritch.myby.co.uk/hf.htm"><FONT
size=4>www.apritch.myby.co.uk/hf.htm</FONT></A><FONT size=4> I would be
interested to hear comments on my proposal for a world wide APRS net on 20m. See
</FONT><A href="http://www.bandscommunications.co.uk/"><FONT
size=4>www.bandscommunications.co.uk</FONT></A><FONT size=4> under the ‘aprs hf
net’ tab.</P>
<P>I think that covers everything for now.</P>
<P>73</P>
<P>Jim, G0JXN</P>
<P><FONT size=2></FONT> </P></FONT></FONT></DIV></BODY></HTML>